Method for preparing barrier meat wrapping base paper

Abstract

This invention provides a method for preparing barrier-type flesh-coated base paper, comprising: mixing softwood pulp and hardwood pulp at an oven-dry weight ratio of (30-40):(60-70), beating the pulp to a freeness of 36-42°SR, and sequentially adding a wet strength agent and a retention aid; after forming the pulp, when the wet paper sheet dryness is 23-30%, using 90-120... The paper is pressed under a linear pressure of kN / m, then dried and creased at 15-22% to obtain the base paper for wrapping meat. Through the synergy of the above processes, the resulting base paper has a density ≥0.60g / cm³, an air permeability of 1.0-5.0μm / (Pa·s), a 60-second Cobb value ≤35g / m² for refined lard (35℃), and a wet tensile strength significantly higher than that of ordinary kitchen paper. This invention effectively solves the problems of easy tearing and oil leakage when conventional kitchen paper is used to wrap fresh meat at a cost close to that of household paper, while also having good air permeability.

Description

Technical Field

[0001] This invention relates to a method for preparing a barrier-type meat-coating base paper. Background Technology

[0002] When purchasing or using fresh meat, poultry, and fish, it is often desirable to simply wrap or cover them to prevent stains or oil from contaminating other items. A convenient packaging method is to directly use kitchen paper for wrapping or covering, such as the kitchen paper shown in documents CN102028423A, CN101850636A, and CN101817242A. However, using ordinary kitchen paper to wrap these products, especially fresh meat, presents the following problems: 1. Regular kitchen paper towels lose a lot of strength when exposed to blood, making them prone to tearing and causing paper fibers to stick to meat, affecting hygiene and appearance; Second, conventional kitchen paper towels are designed to quickly absorb and spread liquids, including grease. This is contrary to the actual need for wrapping meat products, where the goal is to at least slow down the penetration of animal fats and prevent rapid contamination. As a result, grease often penetrates the paper quickly along with blood, contaminating the user's hands and the outer packaging.

[0003] Therefore, there is a lack of paper products in the existing technology that can balance low cost, high wet strength, and effectively delay the penetration of animal fat when wrapping fresh meat. There is an urgent need in the field for an improved solution for this specific use case. Summary of the Invention

[0004] Therefore, the present invention provides a method for preparing a barrier-type flesh-coating base paper to solve the above-mentioned technical problems.

[0005] A method for preparing a barrier-type flesh-coating base paper includes the following steps: S1. Mix softwood pulp and hardwood pulp at an oven-dry mass ratio of (30-40):(60-70), beat the pulp to a freeness of 36-42°SR, and then add wet strength agent and retention aid; S2. After the pulp treated in S1 is formed, it is pressed. The dryness of the wet paper entering the pressing zone is controlled to be 23-30%, and a linear pressure of 90-120 kN / m is used for pressing. S3. The pressed paper is dried and then creped to obtain meat-wrapping base paper. During creping, the creping rate is 15-22%, and the meat-wrapping base paper has a density ≥0.60g / cm³, an air permeability of 1.0-5.0μm / (Pa·s), and a 60-second Cobb value for lard (35℃) ≤35g / m².

[0006] In step S1, the wet strength agent is polyamide epichlorohydrin resin, and the addition amount is 45-60 kg / t oven-dry pulp.

[0007] In step S1, the retention aid includes cationic starch and colloidal silica microparticle retention aid, and the cationic starch and colloidal silica microparticle retention aid are added according to the following steps: S11: Add cationic starch to the slurry at a rate of 3-8 kg / t oven-dry slurry; S12: Add colloidal silica microparticle retention aid 1 minute after adding cationic starch, at a rate of 0.2-0.8 kg / t oven-dry pulp.

[0008] The cationic starch is added to the inlet tank, and the colloidal silica microparticle retention aid is added to the inlet of the slurry pump or before the pressure screen.

[0009] In the slurry, the retention rate of fine fibers and micro-components is greater than or equal to 80%.

[0010] Step S1 further includes adding 0.5 to 1.5% fine fibers before pulping.

[0011] The fine fibers mentioned above are fiber components recovered from the white water used in the system's papermaking process.

[0012] In step S3, after wrinkling, the wrinkle depth is 10-20 μm.

[0013] The step S3 includes a soft calendering step for the meat-wrapping paper.

[0014] The process involves soft calendering of the meat-coating base paper using a linear pressure of 30–60 kN / m and a calendering roller temperature of 60–90°C.

[0015] Beneficial Effects: This invention provides a method for preparing flesh-wrapped base paper, comprising: mixing softwood pulp and hardwood pulp at an oven-dry weight ratio of (30-40):(60-70), beating the pulp to a freeness of 36-42°SR, and sequentially adding a wet strength agent and a retention aid; after forming the pulp, pressing it at a linear pressure of 90-120 kN / m when the wet paper sheet has a dryness of 23-30%; and then drying and creping at 15-22% to obtain flesh-wrapped base paper. Through the synergistic effect of the above processes, the density of the obtained base paper is ≥0.60. With a strength of g / cm³, an air permeability of 1.0~5.0μm / (Pa·s), a 60-second Cobb value of ≤35g / m² for refined lard (35℃), and a wet tensile strength significantly higher than ordinary kitchen paper, this invention effectively solves the problems of easy tearing and oil leakage when wrapping fresh meat with conventional kitchen paper at a cost close to that of household paper, while also having good air permeability. Detailed Implementation

[0016] A method for preparing a barrier-type flesh-coating base paper includes the following steps: S1. Mix softwood pulp and hardwood pulp at an oven-dry mass ratio of (30-40):(60-70), beat the pulp to a freeness of 36-42°SR, and then add wet strength agent and retention aid.

[0017] Specifically, the softwood pulp can be selected from chemical pulp made from coniferous trees such as northern pine, larch, spruce, and fir, preferably bleached sulfate softwood pulp (NBKP). It is understood that the softwood pulp has a length of 2.0 to 4.0 mm. The softwood pulp forms a network skeleton, and during the pulping process, its long fibers are easy to filament and form a huge specific surface area. When drying, it can form a large number of hydrogen bonds with other fibers, thus making a major contribution to the tensile strength, tear resistance, and toughness of the paper.

[0018] The hardwood pulp can be selected from chemical pulps made from hardwood species such as eucalyptus and acacia, preferably bleached sulfate hardwood pulp (LBKP). It is understood that the hardwood pulp has a length of 0.8–1.2 mm, which can effectively fill the gaps in the network skeleton formed by coniferous fibers, thereby improving the uniformity, smoothness, and density of the paper. Furthermore, the fine fibers, mainly formed from hardwood pulp, are retained under the action of retention aids and are embedded and compacted in the gaps during subsequent high-pressure pressing, thus forming a microstructure with fine pores and tortuous channels.

[0019] In addition, pulping should be done to a freeness of 36-42°SR. Studies have found that when the freeness is below the lower limit of 36°SR, the fibers are not fully bonded, the paper structure is loose, the pores are large, and fat can penetrate quickly. When the freeness is above 42°SR, it will lead to excessively high or uncontrollable subsequent tightness, damage the strength of the fiber skeleton, resulting in excessive dust during subsequent creping, and damage to the pore connectivity of the fiber network, resulting in loss of air permeability.

[0020] It is understood that the wet strength agent and retention aid are added in sequence, that is, the wet strength agent should be added first so that the wet strength agent has a longer contact time with the fiber.

[0021] In this embodiment, the wet strength agent is polyamide epichlorohydrin resin (PAE), and the addition amount is 45-60 kg / t oven-dry pulp, preferably 50-55 kg / t oven-dry pulp.

[0022] Furthermore, the retention aid includes cationic starch and colloidal silica microparticle retention aid, and the cationic starch and colloidal silica microparticle retention aid are added according to the following steps.

[0023] S11: Add cationic starch to the slurry at a rate of 3-8 kg / t oven-dry slurry; S12: Add colloidal silica microparticle retention aid 1 minute after adding cationic starch, at a rate of 0.2-0.8 kg / t oven-dry pulp.

[0024] Understandably, by first adding cationic starch, which is adsorbed onto the surface of negatively charged fibers and fine fibers through electrostatic action, it serves three purposes: firstly, it provides a base for subsequent retention aids; secondly, it acts as a dry strength agent to improve the dry strength of the paper; and thirdly, it performs preliminary flocculation, forming larger initial flocs. Then, the flocculation effect of silica microparticles improves the retention rate of fine fibers and micro-components in the pulp. Studies have found that the retention rate of fine fibers and micro-components should reach more than 80% so that they can be more densely embedded in the pores during subsequent high-pressure pressing to form a barrier effect or form smaller capillaries to create capillary resistance.

[0025] Furthermore, the cationic starch is added to the pre-machine tank, and the silica particles are added to the inlet of the slurry pump or before the pressure screen. On the one hand, the slurry is pre-treated with cationic starch and is in a pre-flocculated state when it is at the inlet of the slurry pump or before the pressure screen. On the other hand, the moderate shear force generated by the slurry pump or pumping can help to break up the large and loose flocs formed by the cationic starch and recombine them into small flocs. After the small flocs are formed, they can quickly pass through the pressure screen to remove excessive impurities and enter the headbox to form the web. Since the small flocs have better shear resistance, they can basically remain intact and reach the web, thereby stably achieving a high retention rate. It is understood that silica particles should be avoided in the headbox.

[0026] Furthermore, step S1 also includes adding 0.5 to 1.5% fine fibers before pulping to maintain sufficient fine fibers or small components in the pulp, wherein the fine fibers refer to components with a fiber length of less than or equal to 0.4 mm.

[0027] Furthermore, the fine fibers are fiber components recovered from the white water used in the system's papermaking process.

[0028] S2. After the pulp treated in S1 is formed, it is pressed. The dryness of the wet paper entering the pressing zone is controlled to be 23-30%, and a linear pressure of 90-120 kN / m is used for pressing. Understandably, controlling the dryness of the wet paper entering the press zone to 23-30% serves several purposes. Firstly, at this moisture content, water can fully wet the fiber cell walls, acting as an internal plasticizer, reducing the hydrogen bonding forces between cellulose microfibrils and the rigidity of the fibers themselves. Secondly, the paper web has sufficient strength to withstand high pressure without being crushed, while the fiber network within it possesses good fluidity, enabling it to slip, bend, and undergo irreversible deformation under pressure. Studies have found that when the dryness is below 23%, the paper web is too wet, and under high pressure, water will carry a large number of fine fibers that are not yet firmly bonded, along with chemicals, and be rapidly extruded, disrupting structural uniformity and potentially leading to unstable dehydration in the press zone. Secondly, when the dryness is above 30%, the fiber network hardens due to reduced moisture, entering the elastic deformation-dominant zone. Most of the applied high-pressure energy is stored as elastic potential energy; once the pressure is released, the paper web will experience severe rebound, failing to achieve stable density and potentially causing fiber damage.

[0029] Furthermore, a boot press is used during pressing to allow for higher overall compression work at relatively lower pressure peaks through a wide pressing zone, resulting in a gentler and more uniform structural treatment of the paper web, which is conducive to forming a uniform overall density.

[0030] In addition, using a high linear pressure of 90–120 kN / m can increase the paper web dryness to over 42%, reducing energy consumption in the subsequent drying section. Furthermore, high linear pressure can cause strong compression of the fiber network in a plastic state. The fine fibers with a high retention rate within the fiber network can be tightly embedded and filled under high pressure, and combined with the subsequent drying and creping processes, the paper sheet can achieve a density requirement of ≥0.60 g / cm³. This process not only improves the density of the paper sheet, but more importantly, it narrows and tortuouss the pore channels inside the paper sheet, thereby creating capillary resistance to the high viscosity of animal fats and forming a physical barrier structure.

[0031] S3. The pressed paper is dried and then creped to obtain meat-wrapping base paper. During creping, the creping rate is 15-22%, and the meat-wrapping base paper has a density ≥0.60 g / cm³, an air permeability of 1.0-5.0 μm / (Pa·s), and a 60-second Cobb value for refined lard (35℃) ≤35 g / m².

[0032] In this embodiment, drying is performed using a Yankee drying cylinder.

[0033] In addition, during the wrinkling process, the wrinkling rate should be controlled at 15-22% to form wrinkles with a depth of 10-20 μm. The grooves of this depth of wrinkles can temporarily contain liquids, especially blood-water mixtures. Furthermore, this depth of wrinkles can increase the contact angle of fat droplets, reduce the degree and speed of continuous spread of fat on the paper surface, thereby reducing fat penetration and forming an initial barrier effect.

[0034] Understandably, the processing in steps S2 and S3 ensures that the paper has sufficient air permeability, and controls the air permeability to 1.0–5.0 μm / (Pa·s), so as to meet the micro-permeable environment required for meat preservation on the one hand, and ensure that the pores are small enough to effectively block fat on the other hand.

[0035] Furthermore, after step S3, a soft calendering step is also included for the meat-filling base paper.

[0036] Specifically, the meat-wrapping paper is soft-calendered under process conditions of 30–60 kN / m linear pressure and calender roller temperature of 60–90℃. This process slightly smooths out the most prominent fiber tips caused by wrinkles, making the paper surface smoother and preventing it from sticking to the wet and cold meat. On the other hand, soft calendering does not flatten the main wrinkled structure, thus not substantially affecting the anti-fat spreading ability and internal air permeability imparted by the wrinkles.

[0037] The method is further illustrated below with specific examples. Example

[0038] S1. Raw materials: NBKP:LBKP = 35:65; Pulping: Pulping the mixed slurry to a freeness of 38°SR.

[0039] Wet strength agent (PAE, 52 kg / t), cationic starch (5 kg / t, added to the pulp tank of the paper machine), and colloidal silica microparticle retention aid (0.5 kg / t, added to the inlet of the pulp pump) are added in sequence.

[0040] S2: Valmet NTT paper machine, crescent forming, speed: 1000m / min; The wet paper entering the press zone has a dryness of 25%. Shoe press, with a linear pressure of 110 kN / m.

[0041] S3. Dry and wrinkle the paper sheets to a wrinkling rate of 19% to obtain the final meat-wrapping base paper.

[0042] Comparative Example 1: In S1, cationic starch and silica microparticle retention aids were not added; only the same amount of PAE wet strength agent was added. Otherwise, it was the same as in Example 1.

[0043] Comparative Example 2: In S2, the pressing line pressure is the conventional 60 kN / m, and everything else is the same as in Example 1.

[0044] Comparative Example 3: Commercially available ordinary kitchen paper has a basis weight of approximately 41 g / m².

[0045] The specific test data is as follows: sample unit Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Test methods Quantitative g / m² 42 42 42 41 GB / T 451.2-2023 Tightness g / cm³ 0.63 0.57 0.55 0.50 GB / T 451.3-2002 Breathability μm / (Pa·s) 2.8 6.5 7.8 ＞15.0 GB / T 458-2008 Wet strength kN / m 3.6 3 2.8 2.0 GB / T 465.2-2008 Water Cobb value g / m² 85 88 90 95 GB / T 1540-2002 (25℃) Soybean oil Cobb value g / m² 46 50 55 80 GB / T 1540-2002 (25℃) Cobb value of lard g / m² 31 58 65 75 GB / T 1540-2002 (35℃) Infiltration time h ＞3h Approximately 1.5 Approximately 1 ＜0.5 Simulated package test The Cobb values ​​of water, soybean oil, and lard were all determined according to the test method of GB / T1540~2002 "Determination of water absorption of paper and paperboard (Cobb method)". The test area was 100 cm², 100 mL of test solution was poured in, and after standing for 60 seconds at the specified temperature, the residual liquid on the surface was removed and weighed. The weight gain per unit area (g / m²) was calculated. The test solution for lard Cobb value was grade 1 refined lard that conformed to GB / T 8937, with an acid value ≤1.0 mg KOH / g and a peroxide value ≤5.0 mmol / kg. It was melted and kept warm in a water bath at 35±1℃.

[0046] Penetration time: Cut a piece of paper into 150mm×150mm pieces, wrap 50g of chilled fresh pork filling with a fat content of about 20%, place it in a 4℃ refrigerator, observe the outer surface of the paper every 30 minutes, and record the time when the first obvious visible oil stains appear.

[0047] As can be seen, Example 1 achieves the best balance of density ≥0.60 g / cm³, air permeability 1.0~5.0 μm / (Pa·s), and lard Cobb value ≤35 g / m² through a complete process (high-efficiency retention aid + high-strength pressing + creping). Compared with conventional kitchen paper, the base paper of Example 1 significantly improves the barrier properties and wet strength against fresh meat fat while maintaining the cost characteristics of household paper. In other words, the present invention can achieve excellent performance in the special scenario of wrapping meat.

[0048] In addition, it can be seen that Comparative Example 1, which lacks retention aids, and Comparative Example 2, which uses conventional linear pressure, cannot meet the requirements for blocking animal fat and cannot significantly improve the penetration time. Therefore, steps S1, S2, and S3 must work together to achieve the goal.

[0049] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a barrier-type meat-coating base paper, characterized in that, Includes the following steps: S1. Mix softwood pulp and hardwood pulp at an oven-dry mass ratio of (30-40):(60-70), beat the pulp to a freeness of 36-42°SR, and then add wet strength agent and retention aid. S2. After the pulp treated in S1 is formed, it is pressed. The dryness of the wet paper entering the pressing zone is controlled to be 23-30%, and a linear pressure of 90-120 kN / m is used for pressing. S3. The pressed paper is dried and then creped to obtain meat-wrapping base paper. During creping, the creping rate is 15-22%, and the meat-wrapping base paper has a density ≥0.60g / cm³, an air permeability of 1.0-5.0μm / (Pa·s), and a 60-second Cobb value for lard (35℃) ≤35g / m².

2. The preparation method according to claim 1, characterized in that, In step S1, the wet strength agent is polyamide epichlorohydrin resin, and the addition amount is 45-60 kg / t oven-dry pulp.

3. The preparation method according to claim 1, characterized in that, In step S1, the retention aid includes cationic starch and colloidal silica microparticle retention aid, and the cationic starch and colloidal silica microparticle retention aid are added according to the following steps: S11: Add cationic starch to the slurry at a rate of 3-8 kg / t oven-dry slurry; S12: Add colloidal silica microparticle retention aid 1 minute after adding cationic starch, at a rate of 0.2-0.8 kg / t oven-dry pulp.

4. The preparation method according to claim 3, characterized in that, The cationic starch is added to the inlet tank, and the colloidal silica microparticle retention aid is added to the inlet of the slurry pump or before the pressure screen.

5. The preparation method according to claim 4, characterized in that, In the slurry, the retention rate of fine fibers and micro-components is greater than or equal to 80%.

6. The preparation method according to claim 3, characterized in that, Step S1 also includes adding 0.5 to 1.5% fine fibers before pulping.

7. The preparation method according to claim 6, characterized in that, The fine fibers are fiber components recovered from the white water used in the system's papermaking process.

8. The preparation method according to claim 1, characterized in that, In step S3, after wrinkling, the wrinkle depth is 10-20 μm.

9. The preparation method according to claim 1, characterized in that, The step S3 is followed by a soft calendering step of the wrapping paper.

10. The preparation method according to claim 9, characterized in that, The meat-filled base paper is soft-calendered under process conditions of 30-60 kN / m linear pressure and calender roll temperature of 60-90℃.